Magnetic Resonance Imaging of Pelvic Masses: A Compartmental Approach

Author’s Accepted Manuscript MR Imaging of Pelvic Masses: A Compartmental Approach Kiran Gangadhar, Abhishek Mahajan, Nilesh Sable, Puneet Bhargava www.elsevier.com/locate/enganabound

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S0887-2171(16)30099-3 http://dx.doi.org/10.1053/j.sult.2016.11.004 YSULT736

To appear in: Seminars in Ultrasound, CT, and MRI Cite this article as: Kiran Gangadhar, Abhishek Mahajan, Nilesh Sable and Puneet Bhargava, MR Imaging of Pelvic Masses: A Compartmental Approach, Seminars in Ultrasound, CT, and MRI, http://dx.doi.org/10.1053/j.sult.2016.11.004 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

MR IMAGING OF PELVIC MASSES: A COMPARTMENTAL APPROACH. Kiran Gangadhar MD1; Abhishek Mahajan, MD2; Nilesh Sable, MD2; Puneet Bhargava, MD1.

1-Department of Radiology, University of Washington School of Medicine, Box 357115, 1959 Pacific Street, RR-215, Seattle, WA 98195 2-Department of Radiology, Tata Memorial Hospital, Dr. E Borges Road, Parel, Mumbai, India 400 012

Address Correspondence to: Puneet Bhargava MD Associate Professor, Department of Radiology, University of Washington School of Medicine, 1959 NE Pacific Street, Room BB308, Box 357115, Seattle, WA 98195-7115 Phone: (206) 598-1448 Fax: (206) 598-0252 Email: [email protected]

Authors' contributions The authors were involved in case collection and documentation.

Acknowledgements None.

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Disclosures Puneet Bhargava, Editor-in-chief, Current Problems in Diagnostic Radiology, Elsevier Inc.

Consent NA

Human and animal rights Not applicable

Key words: Pelvic masses, MRI, Magnetic resonance imaging, Approach

Abbreviations: MRI-Magnetic resonance imaging, T1WI-T1 weighted imaging, T2WIT2 weighted imaging, DWI-Diffusion weighted imaging.

MR IMAGING OF FEMALE PELVIC MASSES: A COMPARTMENTAL APPROACH

ABSTRACT: Magnetic resonance (MR) imaging is often “one stop shop” for evaluating female pelvic masses which helps in diagnosis, staging and restaging of these tumors. A pelvic mass can arise from any tissue present within the pelvis. While most masses in the female pelvis arise from the reproductive organs, masses may also arise from the gastrointestinal

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tract, urinary system, adjacent soft tissues, peritoneum etc. It may not always be possible to determine the site of origin or distinguish these masses based on imaging characteristics. However, familiarity with the clinico-pathologic and MR imaging features of most common pelvic masses helps in narrowing the differential diagnosis. Diagnosis of these masses needs a holistic approach as required for any tumor including clinical history, laboratory data and imaging characteristics. We focus on MR imaging characteristics of commonly encountered pelvic masses. A compartmental imaging approach is discussed in this review article which helps in identifying and characterizing these masses.

INTRODUCTION: Female pelvic masses most commonly originate from the reproductive tract, although they may arise from other organs and tissues in the pelvis, such as the gastrointestinal or urinary tracts. Many pelvic masses are common entities such as uterine leiomyoma, ovarian cysts, and dermoid tumors. However, less common tumors such as uterine sarcomas, fallopian tube carcinomas, peritoneal neoplasms, gastrointestinal neoplasms, and metastatic disease should also be considered. Accuracy in diagnosis and staging is extremely important because of the obvious therapeutic implications. The evaluation of a pelvic mass begins with clinical history and physical examination. Imaging characterization often starts with ultrasound and finally proceeds to magnetic resonance imaging. Each of these modalities have a role in the work-up of pelvic masses and has its own advantages and disadvantages. Ultrasound is the least invasive and most cost-effective diagnostic tool. MRI demonstrates excellent soft tissue contrast resolution,

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resulting in accurate tissue characterization and improved anatomic delineation and has been shown to be superior to ultrasound for characterizing adnexal masses (1, 2). Other invasive techniques to accurately diagnose pelvic masses include, laparoscopy, hysteroscopy, laparotomy and vaginal hysterectomy. These procedures are performed only if the imaging diagnosis is inconclusive and are at least 2 to 8 times more expensive than imaging diagnosis. Moreover, more than half of the pelvic masses deemed suspicious by clinical examination, tumor marker (CA 125 level) and imaging (ultrasonography) are benign(3). Overall, MRI may be more cost-effective and noninvasive imaging modality as it not only avoids unnecessary surgical procedures but also the risk of peritoneal spillage of cancer from cyst rupture during these procedures (4, 5). The female pelvis can be divided into three compartments for practical purposes: the anterior, middle and posterior compartment.

Table-1 (Figure 1). Anterior

Middle

Posterior

Combined

Urinary bladder

Uterus and cervix

Recto sigmoid bowel

Peritoneum

Soft issue in

Adnexal structures

Soft tissue in pre-

Soft tissue in

sacral space

retro-vesical

retropubic space,

space, rectouterine space

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MRI protocol and General MR Tissue characterization A comprehensive MR imaging examination in a case of pelvic mass includes; T1weighted, T2-weighted, T2-weighted with fat saturation, diffusion weighted imaging and dynamic post contrast imaging. At our institution, the following sequences are used as the standard technique for MRI pelvic mass protocol: 1. HASTE Coronal Abdomen and pelvis 2. Axial T1 whole pelvis 3. Axial T2 Fast spin echo (FSE) Fat saturated (FS). 4. High resolution (HR) Axial, Coronal and Sagittal T2. 5. Axial THRIVE FS without and with contrast 6. Coronal THRIVE with FS post contrast

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Table 2: Tissue

MR characteristics

Common etiology

Simple fluid

Hypointensity on T1;

Functional ovarian cyst, cystic

Hyperintensity on T2; -ve

tumors of ovary, epidermoid

enhancement

cysts, duplication cyst of rectum

Complex fluid

Hypointensity on T1 and

Cystic ovarian neoplasms,

variable if there is

hydrosalphinx, pyosalphinx,

proteinaceous contents; hyperintensity on T2; +/- ve enhancement Blood

Depends on stage hemorrhagic

Hematoma, hemorrhagic cyst,

degradation products.

endometriosis, ectopic

Hyperintensity on T1; Variable

pregnancy, hematosalpinx,

intensity on T2; no enhancement Mucin

Hypo/hyperintensity on T1;

Mucinous tumors of ovary

hyperintensity on T2; peripheral Fat

Hyperintensity on T1;

Dermoid, lipoma,

intermediate intensity on T2; -

liposarcoma, lipoleiomyoma.

ve enhancement Myxoid tissue

Hypo/isointensity on T1;

Angiomyxoma, myxoid

hyperintensity on T2; +ve

degeneration of fibroid,

enhancement

neurogenic tumors, myxoid liposarcoma

Fibrous tissue

Isointense on T1; hypointense

Fibroid, Scar tissue, Solid

on T2; +ve enhancement

endometriosis, Brenner tumor, Fibroma or fibro-thecoma of ovaries.

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ANTERIOR COMPARTMENT MASSES Urinary bladder masses Bladder diverticulum Bladder diverticulum is an outpouching of the wall through which mucosa herniates. It can be congenital or acquired in nature. Congenital diverticulum arises near vesicoureteral junction and is called as ‘Hutch’ diverticulum. Most common acquired cause is bladder outlet obstruction, which could be due to stricture or a mass. On MRI, a diverticulum appears as focal outpouching with signal intensity similar to urine (Fig 2a2b). Signal characteristics can be variable depending upon presence of debris (Fig 2a-2b), stone or rarely a malignant mass (Fig 2c-2d) (6).

Urethral diverticulum A urethral diverticulum occurs in women in the 3rd-7th decade of life, with an estimated prevalence of 0.6-6%. Risk factors for acquired urethral diverticulum include repeated infection of the periurethral glands, and trauma from the prior vaginal delivery or vaginal/urethral procedures. The most widely accepted theory of etio-pathogenesis is rupture of a periurethral gland into the urethral lumen after chronic obstruction and recurrent infection (7). On MRI, a urethral diverticulum appears as unilocular or multilocular cystic lesion with hypointensity on T1 and hyperintensity on T2-weighted images (Fig 3a-3b). Signal characteristics can be variable depending upon presence of hemorrhage, debris,

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stone or a mass. A diverticulum can be seen involving complete or incomplete urethral circumference, called as “saddle bag diverticulum” (Fig 3). Intravenous gadoliniumbased contrast material administration helps in the detection of inflammation or a rare intra-diverticular malignancy (8).

Urinary bladder cancer The incidence of urinary bladder cancer in women is increasing, however, three to four times lower than in men. Smoking is the most important known factor for bladder cancer in women. Occupational exposure and urinary tract infections are additional risk factors bladder cancer. Unfortunately, bladder cancer is more often found at advanced stages in females (9). Most of the bladder tumors are transitional cell carcinomas constituting around 90%. Squamous cell carcinomas account for 6%–8% of all bladder cancers and rarely adenocarcinomas occur as urachal malignancy (Fig 4a-4b) (10). MR has demonstrated superior performance in local staging of the tumor, specifically regarding intramural tumor invasion and differentiating between muscle-invasive and non-muscle-invasive disease that has surgical implication. On MRI tumor appears isointense on T1WI (Fig 4c), slightly hyperintense (Fig 4d) compared to muscle on T2WI and demonstrate diffusion restriction (Fig 4e). These lesions show early enhancement on post contrast sequences (Fig 4f) (11).

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MIDDLE COMPARTMENT MASSES Uterine masses Fibroid (Leiomyoma) Fibroids are the most common benign tumors arising from the uterine smooth muscle. They occur in 20% of women in the reproductive age group. Although most commonly arising from the body of the uterus, fibroids may also arise from the cervix and also can be located in the broad ligament. They are classified as submucosal, intramural and sub serosal depending upon location within the uterus (Fig 5a-5f); most common being intramural. On MR, fibroids are typically well-circumscribed masses with homogenous low signal intensity in both T1-weighted and T2-weighted images (Fig 5a-5b) with homogenous arterial enhancement. Leiomyomas with hyaline or calcific degeneration cannot be differentiated distinctively on MR, however, the changes could represent as foci of nonenhancement. Those with cystic degeneration tend to have high signal intensity on T2weighted images; whereas, myxoid degeneration is seen as high T2-weighted areas that have minimal enhancement. Red degeneration can be seen as peripherally located variable high signal intensities on T1-weighted images, due to the presence of blood products(12). Very rarely fibroids can have microscopic or macroscopic fat and are called as ‘lipoleiomyoma’ (Fig 5g-5h) which can be distinguished using T1 opposed phase or fat saturated sequences respectively (13) .

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Adenomyosis Adenomyosis is ectopic location of endometrial glands and stroma in the uterine myometrium surrounded by hypertrophic and hyperplastic smooth muscle. It is one of the most common uterine benign condition after fibroid and is noted in 20% to 30% of the general female population, and in 5-70% of hysterectomy specimens (14, 15). There are two types of adenomyosis; diffuse and focal. On MRI, the diffuse form presents as symmetric enlargement of uterus with thickening of the interface between myometrium and endometrium called as “junctional zone” (JZ) by more than 12 mm. The JZ also appears indistinct (Fig 6a). A JZ < 8 mm in thickness, excludes adenomyosis. Whereas, a JZ thickness between 8 and 12 mm, falls in the grey zone and diagnosis of adenomyosis depends on history and other imaging findings. On post contrast images (Fig 6b), areas of adenomyosis exhibit heterogeneous enhancement compared to the myometrium and not infrequently the entire myometrium appears heterogeneous.

Furthermore, adenomyosis is predominantly T2 hypointense

with scattered subcentimeter foci of T2 and T1 hyperintensity that represent cystic/hemorrhagic components (Fig 6a) (16). The focal form (Fig 6c-6d) is rare and presents as a round lesion either contiguous or separate from the JZ. The latter can often be confused with a uterine fibroid. However, adenomyosis often demonstrates T2W and T1W high intensity foci (corresponding to small cystic and hemorrhagic components respectively) and fibroids typically have large peripheral vessels(17). Needless to say, these entities can coexist and it may not be possible to differentiate from each other in all cases.

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Endometrial polyp Endometrial polyps are one of the common benign entities of uterus consisting of nodular protrusion of endometrium into the uterine cavity with stroma and endometrial glands. Tamoxifen therapy is one of the risk factor, which can lead to endometrial polyps in 8 to 36% of postmenopausal females treated with this drug (18). They can occur as a part of endometrial hyperplasia but are frequently seen in isolation. They can be pedunculated and can prolapse into the endo-cervical canal (Fig 7a-7d) (17). On MRI polyps appear as intermediate signal intensity endometrial nodular lesions on T1-weighted images and exhibit heterogeneous hyper intense signal on T2-weighted images (Fig 7c-7e) with late enhancement greater than the myometrium on post contrast sequences (Fig7d-and 7f). Endometrial polyps more commonly exhibit intra-tumoral cystic areas and fibrous core than endometrial cancers, however myometrial invasion and necrosis are more specific features of carcinomas (19).

Cervical cancer Cervical cancer is one of the most common gynecological malignancy affecting women in reproductive age, with incidence of five hundred thousand new cases worldwide, which is second only to breast cancer. The cervical cancer risk factors include, HPV infection, smoking, nulliparity, use of oral contraceptives etc. (20). Most of the cervical cancer cases are a result of genital infection with human papillomavirus

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(HPV). HPV vaccines are very effective at preventing infection and disease related to the vaccine-specific genotypes in women with no evidence of past or current HPV infection, with protection lasting for at least 5 years (21). For the past several decades there has been decreasing cervical cancer mortality rates due to widespread use of cytological screening with Pap smear that produced a 60% reduction of cancers in women aged 40, increasing to 80% at age 64 (22). International Federation of Gynecology and Obstetrics (FIGO) staging system is used for staging and management of cervical cancer. MR imaging is an excellent modality for depicting invasive cervical cancer, and it demonstrates 95% of cancers at stage 1B(23). It appears as T2 hyperintense heterogeneously enhancing diffusion restricting mass (Fig 8a-8d) and MR can depict stromal invasion in as high as 80% of cases and also better delineates myometrial invasion with specificity as high as 94% (24) which has management implications(25).

Endometrial cancer Endometrial carcinoma is the most common female pelvic malignancy with the peak incidence occurring around the sixth or seventh decade of life and the seventh most common neoplasm worldwide. The risk factors include genetic predisposition like Lynch II syndrome, nulliparity, diabetes, unopposed estrogen intake, Stein-Leventhal syndrome, and tamoxifen therapy(26). Endometrial carcinoma is commonly seen in postmenopausal women and often present with postmenopausal vaginal bleeding and up to 75% of

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patients can be diagnosed at an early stage disease because of early clinical symptoms (27, 28). Endometrial cancer may demonstrate heterogeneous high signal intensity on T2weighted sequences (Fig 9a) with restricted diffusion on DWI (Fig 9b). It typically shows lesser enhancement compared to the normal myometrium and may show non-enhancing foci of necrosis (Fig 9c and 9d). FIGO staging system is used; T2-weighted images provide optimal depiction of the uterine zonal anatomy and helps in assessing the junctional zone involvement which is critical in distinguishing noninvasive (Stage IA), superficial (Stage IB), or deep (Stage IC) myometrial invasion (29, 30). Myometrial invasion is an important predictor of nodal involvement; >50% myometrial invasion increases the risk of lymph node involvement by 6 to 7 fold. Hence, characterization of myometrial invasion is important for surgical planning (31).

Uterine sarcomas Uterine sarcomas are rare tumors of mesodermal origin, constituting only 2–6% of uterine malignant tumors. Histo-pathologically, they are classified into four common variants:

leiomyosarcoma,

endometrial

stromal

sarcoma,

adenosarcoma,

and

carcinosarcoma. (32). FIGO staging system is used for these tumors which slightly vary for leiomyosarcoma, endometrial stromal sarcoma and adenosarcoma. Carcinosarcomas are staged in a similar manner as endometrial cancer (33).

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Table 3: Key differences in uterine sarcoma FIGO staging of uterine sarcomas(33). Leiomyosarcomas and endometrial stromal Adenosarcomas sarcomas (ESS) Stage I

Stage I

IA- <5cm

IA-Tumor

limited

endometrium/endocervix

to with

no

myometrial invasion IB- >5 cm

IB-Less than or equal to half myometrial invasion IC- More than half myometrial invasion

MRI helps in staging of these tumors. MRI features that differentiate these with more common tumors like leiomyoma or endometrial cancer include aggressive growth, heterogeneous (Fig 10a-10f) appearance, lesser degree of enhancement, higher incidence of lymphatic and vascular invasion, increased foci of necrosis, peripheral hypointense rim on T2-weighted images, and irregular enhancing margins (34-37).

Adnexal masses Most adnexal masses are benign; cystadenomas are the most common masses in postmenopausal women whereas functional cysts are most common in premenopausal women. There is 5% to 10% lifetime risk of surgery for a suspected adnexal mass with 13% to 21% of these masses being malignant (38). MRI is highly sensitive and specific for identifying malignant adnexal lesions (39, 40). Thomassin-Naggara et al, (37) proposed a preliminary MR scoring system called ADNEX MR SCORING system for determining the probability of malignancy in an adnexal mass depending up on imaging

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characters; An adnexal mass which is purely cystic mass, purely endometriotic, purely fatty like dermoid, without wall enhancement and which shows low b = 1000 sec/mm2– weighted and low T2-weighted signal intensity within solid tissue if present, was given a score of 2 and was termed benign lesion. An adnexal lesion with presence of solid tissue with Type I progressive enhancement curve was given a score of 3 and was termed probable benign mass. An adnexal mass with a solid enhancing tissue with type II plateau enhancement curve was given a score of 4 and was called indeterminate mass. A lesion with a solid enhancing tissue with type III plateau enhancement curve and or with peritoneal implants was given a score of 5 which was labelled as probable malignant mass.

Functional ovarian cysts A functional ovarian cyst is defined as a cyst of ovarian origin with no malignant potential. A vast majority of ovarian cysts detected on imaging are functional cysts that include ovarian follicular cysts, corpus luteum cysts and theca lutein cysts (41). On MRI, these cysts are hypointense on T1WI and hyper intense on T2WI without foci of nodular or septal enhancement (Fig 11 a-11b). These cyst can range from simple unilocular appearance or may have mildly complex features such as few internal septations without nodularity(42).

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Hemorrhagic cysts Hemorrhagic ovarian cysts result from hemorrhage into a corpus luteum or other functional cyst and typically resolve within six to eight weeks. MRI features vary depending on the age of the hemorrhage (Fig 12a and 12b). These are typically hyperintense on T1- and T2-weighted imaging. The MRI signal evolves from the center of cyst to the periphery depending on the stage and duration of hemorrhage. These cysts show no enhancement(43). A follow-up MRI or ultrasound is recommended after 6 to 12 weeks for confirmation of cyst resolution (44).

Endometriosis Endometriosis affects up to 45% of women in reproductive age presenting with chronic pelvic pain, dysmenorrhea, dyspareunia, and infertility. There are three forms of endometriosis; a. Ovarian (endometrioma), b. Peritoneal and c. Deep. Each of these type have different imaging characteristics.

Deep pelvic endometriosis is described as the

subperitoneal invasion that exceeds 5 mm depth. Deep form can affect uterosacral ligaments, rectovaginal septum, retrocervical region, vagina, rectum, uterine tract and other extra-peritoneal sites(45). Ovarian lesions (Fig 13a-13f) are the most common location of endometriosis. “T2 Shading” (Fig 13b) is a specific sign of endometrioma on MRI; it is caused by old blood products, which contain extremely high iron and protein concentrations. These hemorrhagic cysts typically show high signal intensity on T1-weighted images (Fig 13d) and variable low signal intensity on T2-weighted images (Fig 13a-13c). Endometrioma 16

can consist of solid components, thick septa, and fluid-fluid levels which do not enhance on post contrast images (Fig 13e). However, enhancing components can be seen when there is malignant transformation in to endometriod or clear cell ovarian tumors (46, 47). On the other hand, deep form especially involving uterosacral ligaments or the vaginal or rectal wall

can be seen as nodular foci showing hypointensity on T2-weighted

images(48).

Ovarian Neoplasms Ovarian cystic masses represent a spectrum of neoplasms including benign, borderline and high grade type depending up on histopathology. Ovarian tumors can be classified as epithelial, germ cell, sex cord–stromal, or metastatic. Epithelial tumors are the most common histopathologic type of malignant ovarian tumor (85% of cases)(49). The most common type of ovarian malignancy is serous carcinoma (approximately 40% of cases)(50) .

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Table 4: Ovarian tumors overview (49, 51-53) Tumor type

Incidence/ Prognosis

Risk factors

Imaging features

Surface epithelial

65-70%

Increased age

-Serous

5 year

-Mucinous

Early menarche.

Benignthin walled cystic lesions without any evidence of soft tissue components.

survival rate

-Brenner -Endometriod -Mixed

Stage I89%.

-Undifferentiated Stage II70%. Stage III36%.

Late menopause. Nulliparity. Family history

Cystadenocarcinomas are usually larger, BRCA1/BRCA more complex multi-locular masses which contain soft tissue papillary projections, 2 mutations. enhancing nodules, malignant ascites with HNPCC peritoneal nodularity. (Lynch II Brenner tumors –solid low signal intensity syndrome. masses on both T1 and T2 weighted images. Pelvic inflammatory disease.

Stage IV17%

Hormone replacement therapy.

germ cell tumors

15-20%.

Similar

-Teratoma

account for most of the hormonally active ovarian tumours

-Dysgerminoma -Endodermal sinus tumor -Choriocarcinoma

Mucinous cystadenomas are typically multilocular. Serous cystadenoma are most commonly unior bilocular;

Fat is of high signal on T1-weighted MR images and is most effectively distinguished from by frequency selective fat saturation. A fat-fluid interface is highly characteristic of a cystic teratoma

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Sex cord–stromal

5-10%

Similar

Ovarian fibromas are well circumscribed solid tumors which demonstrate low signal intensity on both T1- and T2-weighted images, with minimal enhancement

Variable

Similar

Metastases to the ovary are usually bilateral and may be solid, partially solid and cystic, or occasionally as a multiloculated cystic lesion.

-Fibroma -Sertoli-Leydig cell tumors -Granulosa theca cell tumor Metastasis

Benign ovarian neoplasms Benign epithelial tumors are commonly seen in young women. Serous and mucinous tumors are the two most common neoplasms in this category. Serous cystadenomas occur between 20 to 50 years of age and account for up to 25% of benign ovarian neoplasms. They can be bilateral in 12– 23% of the cases (54). Serous cystadenomas are usually thin walled, unilocular or rarely multilocular cystic lesions showing hypointensity on T1- and hyper intensity on T2-weighted images without postcontrast enhancement (Fig 14a and 14b). Compared to the mucinous cystadenomas, serous tumors are smaller with a greater tendency of bilateral involvement (55). Mucinous cystadenoma are typically multicolular with variable T1 signal intensity depending on presence of hemorrhage or mucin. Also, the T2 signal intensity varies within these lesions depending upon the hydration of the mucin (53). Ovarian dermoid cyst (mature cystic teratoma) is the most common ovarian tumor of germ cell origin accounting for 10-20% of all ovarian masses and is also the most

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common benign ovarian tumor in women less than 20 years old. Peak incidence is seen at 30 years of age and 90% are unilateral (56, 57). These tumors are composed tissues derived from two or more embryonic germ cell layers lined by squamous epithelium and are filled with sebaceous material, hair follicles, skin glands, muscle and teeth (58). MRI helps in making a specific diagnosis by demonstrating macroscopic fat tissue with high signal on T1-weighted and T2-weighted images (Fig 14c). A fat saturated sequence (Fig 14d) enables differentiation of cystic teratoma from other lesions showing T1 hyperintensity like endometrioma or hemorrhagic cyst (59) .

Malignant ovarian masses Ovarian cancer represents the sixth most common cancer among women in the world, and has highest mortality per year than any other cancer of the female reproductive system. Established risk factors for ovarian cancer include age and having a family history of the disease and other potential risk factors are postmenopausal hormone-replacement therapy, cigarette smoking and alcohol consumption (60). On MRI, malignant ovarian tumors demonstrate solid or nodular foci, papillary projections and thick septa (>3 mm) in a cystic lesion (Fig 15a-15c). Extra-ovarian spread is indicated by peritoneal or mesenteric/omental nodularity which can be seen as omental caking, local pelvic wall invasion and lymphadenopathy. MRI features most predictive of malignancy are papillary projections in a cystic lesion, size greater than 6 cm, and necrosis in a solid lesion (53, 61). Ascites (Fig15d) is the least predictive of all features as it can be seen in many benign conditions (62).

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Metastasis The ovaries are one of the common sites for metastasis. The most common primary sites include the stomach, colon, breast, lung and the genitourinary tract. Rarely. ovarian metastasis can be the initial manifestation of some primary tumors of the gastrointestinal tract origin (63). Krukenberg tumors (Fig 16) are a type of metastatic ovarian tumors, that are usually bilateral with predominantly solid morphology and show microscopic infiltration of signet ring cells (64). The colon and stomach are the most common primary sites for Krukenberg tumors, followed by the breast and lung (65). On T1 and T2- weighted MR images (Fig16a and 16b), the solid tumor components typically show heterogeneously low or high signal intensity depending on presence of fibrous or edematous connective tissue respectively. On T1-weighted post contrast MRI (Fig 16c), the solid components usually demonstrate homogeneous enhancement (66).

Other adnexal lesions Some benign complex adnexal lesions of tubal pathology including, hydrosalphinx, pyo-salphinx or tubo-ovarian abscess are assessed using MRI as a second line modality, especially when these are indeterminate on pelvic ultrasound.

It is

important to differentiate a dilated tube from ovarian cysts. Several features are helpful like incomplete folds, an oval or elongated shape, and wall deformities such as “waists”

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or “beaks” depending on the type of convolution (67, 68) .These tubal lesions may appear complex with mural nodules that represent pus, debris or fibrotic mucosal plicae.

Table 5: Uterine

Adnexal

Benign-Leiomyoma,

Adenomyosis, Benign-Functional cysts, benign neoplasms of ovary, Hemorrhagic cysts, Endometriosis,

Endometrial polyp

hydrosalphinx. Malignant-Cervical

cancer, Malignant-Malignant

endometrial cancer, uterine sarcomas.

ovarian

masses,

Metastasis (Kruckenberg tumor).

POSTERIOR COMPARTMENT MASSES Rectal Carcinoma Rectum is involved in up to 65% percent of all colorectal cancers and 98% of these are adenocarcinoma (69). MRI plays a crucial role in local staging of rectal cancer and guides management (70-72). High-resolution images are obtained in the axial and coronal planes and they are angled to the plane exactly perpendicular and parallel to the tumor axis. Coronal plane help in identifying the relationship of low rectal tumors to the internal and external sphincter. Sagittal T2 weighted images help to assess the relationship of the tumor to the peritoneal reflection (73, 74). MR accurately describes 22

important features such as rectal anatomy with T staging (Fig 17a), tumor distance from the anal verge, tumor involvement of anal sphincter complex, nodal status specifically mesorectal and pelvic lymph node involvement, circumferential resection margin and extramural vascular invasion (Fig 17e), all of which have management implications (75). On MRI, rectal cancer appears as T2 intermediate signal intensity tumors (Fig 17b) with post contrast enhancement (Fig 17c) and diffusion restriction (Fig 17d). Pelvic and mesorectal nodes can be assessed on, T2-weighted images and post contrast sequences; although, are better visualized on diffusion-weighted sequences (Fig 17d and 17e) (74, 76).

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Table 6-Rectal cancer brief review (75, 77) . TAnatomical stage considerations

MR findings

Management/Prognosis

T1

confined to the T2 hypointense tumor confined to Local excision/ local radiation if mucosa and submucosa surgery is contraindicated submucosa

T2

tumors invade T2 hypointense tumor invading -Local resecton, consider the muscularis MP, but not extending beyond transabominal resection. propria (MP) MP. -Extramural vascular spread is a key factor in determining prognosis and stratifying patients for preoperative therapy even in T2 stage tumors.

T3

Lesion extending beyond the muscularis propria.

In stage T3, the muscularis propria is completely disrupted and cannot be clearly distinguished from the perirectal fat.

T3a- < 1mm invasion beyond -A positive circumferential resection margin (CRM) is MP. defined as mass extension within T3b- more than 1 mm of the mesorectal fascia. or equal to 1mm5mm invasion -Positive CRM margins can also be due to tumor deposits, beyond MP. extramural vascular invasion or T3c- >5-15mm suspicious lymph nodes within 1 invasion beyond mm of mesorectal fascia. MP.

Chemo-radiation followed by Total mesenteric excision (TME). -risk of metastatic disease increases as the tumor spread beyond 5 mm of MP. -CRM involvement is an important independent prognostic factor for local recurrence and poor survival.

T3d>15mm invasion beyond MP. T4a

Lesions peritoneal invasion.

with Sagittal T2 images are helpful for Chemoradiation followed by TME. assessing peritoneal invasion.

T4b

Involvement of Extension into urinary bladder, Chemotherapy and radiation therapy adjacent organs vagina or uterus, pelvic sidewalls. followed by TME. Locally advanced rectal cancer has a poor prognosis because of the high frequency of metastasis and local recurrence.

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Rectal GIST Gastrointestinal

stromal

tumors

(GISTs)

are

the

most

common

mesenchymal neoplasms of the gastrointestinal tract and rectal GIST accounts for up to 4% of these. GISTs arise from the interstitial cells of Cajal, and over 90% of

these

tumors

show

a

mutation

in

the

tyrosine

kinase

proto-oncogene, CD117(c-kit) which is the primary target for therapy using a smallmolecule tyrosine kinase inhibitor , such as imatinib mesylate (STI571) (78, 79). On MRI (Fig 18a and 18b), T1 and T2 signal intensity varies depending on intratumoral necrosis, cystic or hemorrhagic changes. These tumors can be endoluminal or exophytic, are usually solid and the enhancement pattern depends on the size of the tumor. Smaller tumors tend to show homogenous enhancement whereas larger ones show heterogeneous enhancement pattern (Fig 18c and 18d). Large tumor size

with

intratumoral cystic changes and a low mean ADC value of the solid portion (indicative of high cellularity), are very helpful imaging features for predicting the higher malignant potential of a GIST (80).

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Tail gut cyst Tail gut cysts are common tumors in the presacral region, these are remnants of embryonic hindgut and usually benign, although malignant transformation has been described (81, 82). Uncomplicated cysts exhibit low signal intensity on T1-weighted and high signal intensity on T2-weighted images (Fig 19a) without diffusion restriction (Fig 19b). Complex cysts can appear multilocular, show T1 high signal intensity due to presence of mucin and can appear hypointense

on T2-weighted images due to

hemorrhage or keratin (83). Although malignant transformation is rare, presence of a solid enhancing nodule should raise the concern for malignant transformation. . Complete excision of the entire cyst is necessary to prevent recurrence (84).

Nerve sheath tumor (schwannoma) Sacral schwannoma (Fig 20a-20d) is a benign tumor arising from the sacral nerve root sheaths (85). Sacral region is the second most common site for schwannoma after the mandible. Imaging does not help in differentiation between benign and malignant tumors (86, 87). The main differentials for sacral schwannoma are chordoma and giant cell tumor. Bone erosion instead of bone destruction, cystic areas and absence of adjacent muscles or sacroiliac joints involvement are favorable for schwannoma (88).

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Table 6: Key features of schwannoma, chordoma and giant cell tumor of sacrum. Sacral Tumor

General

Sacral Shwannoma

Arise from Heterogeneously Heterogeneously Intense nerve sheath hypo to hyperintense on heterogeneous composed of hyperintense fluid-sensitive enhancement schwann (diffuse, sequences cells without peripheral or nodular fibrous septa patterns)

Sacral chordoma

arises from development al embryonic remnants of the notochord

Sacral giant locally aggressive, cell tumor potentially malignant bone neoplasm

T1WI

T2WI

Enhancement

high signal intensity on T1WI because of mucoid intercellular material separated by fibrous bands

marked brightening Moderate on T2WI with inhomogeneous multiple iso signal- enhancement intensity septa

Low to intermediate heterogeneous signal intensity, inhomogeneous

Low signal inhomogeneous intensity on T2WI enhancement blood degradation products. Fluidfluid levels can be seen when there is aneurysmal bone cystic component.

COMBINED COMPARTMENT MASSES Most of the malignant masses can involve more than one compartment. Some of these are just extensions from abdominal organs into the pelvis especially lesions like metastasis, lymphoma, peritoneal malignancies and retroperitoneal /pelvic sarcomas (8991).

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CONCLUSION: Pelvic masses may present in a female at any age and most of the pelvic masses originate from the genital tract. Fortunately, most masses are benign. Even though ultrasound is the initial diagnostic tool, MRI plays a crucial role in accurate noninvasive characterization of these masses. Knowledge of key diagnostic features of these masses on MR is important. A tailored compartmental approach helps in anatomic localization and narrowing the differential diagnosis.

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FIGURE LEGENDS Figure 1-Pictoral depiction of compartments of pelvis. Figure 2- Urinary bladder diverticulum: Fig 2a-Axial T2-weighted images shows right inferolateral wall diverticulum with dependent T2 hypo-intense debris showing no contrast enhancement in post-contrast T1WI (Fig 2b). Fig 2c-Transverse US pelvis and Fig 2d-Axial CECT pelvis: Another patient with a hyperechoic malignant mass (arrow) on US which enhances on CT (arrow). Figure 3- Urethral diverticulum: Fig 3a-Axial T2-weighted image shows a periurethral complex cystic lesion with ‘saddle bag’ appearance. Fig 3b-Axial post contrast T1-weighted images with fat saturation shows T1 hypo-intense lesion showing mild diffuse wall enhancement without nodular enhancing foci. Figure 4- Urinary bladder cancer: Fig 4a-Axial post-contrast T1-weighted image showing enhancing mass in the antero-superior bladder wall representing urachal 33

adenocarcinoma showing hypointensity on T2-weighted imaging (Fig 4b). Also note ascites in the pelvis secondary to systemic cause. Fig 4c- Axial T1-weighted and Fig 4d Axial T2-weighted images showing infiltrative transitional cell bladder cancer extending into peri-vesicle fat and anterior abdominal wall (arrows). Fig 4e-Axial diffusion weighted image showing diffusion restriction and Fig 4f-Axial post-contrast T1-weighted image showing heterogeneously enhancing mass. Figure 5- Lieomyoma: Intramural leiomyoma; Fig 5a-Sagittal T2-weighted and Fig 5bAxial T2-weighted images showing T2 hypointense intramural uterine masses. Submucosal leiomyoma; Fig 5c-Sagittal T2-weighted and Fig 5d-Axial post contrast images showing submucosal fibroid in the endometrial canal (long arrows in both figures) showing intense enhancement. Shorter arrows and arrowhead in Fig 5c and Fig 5d are pointing towards intramural fibroids. Subserosal fibroid; Fig 5e-Coronal T2-weighted and Fig 5f-Coronal T1-weighted images showing left subserosal fibroid presenting as adnexal mass. Lipoleiomyoma; Fig 5g-Axial in-phase and Fig 5h- Axial out of-phase images showing areas of microscopic fat with signal drop in out of phase image. Figure 6- Adenomyosis: Diffuse adenomyosis; Fig 6a-Sagittal T2-weighted and Fig 6bSagittal post contrast T1-weighted images showing symmetric increase in size of uterus with indistinct junctional zone (arrow heads in fig 6a) and foci of T2 hypo-intensities and heterogeneous enhancement.

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Focal adenomyosis; Fig 6c-Sagittal T2-weighted and Fig 6d- Sagittal post contrast T1weighted images showing anterior uterine wall mass like area of adenomyosis with indistinct junctional zone and foci of hyper-intensity on T2 associated with heterogeneous iso enhancement. Figure 7- Endometrial polyp: Fig 7a-Sagittal T2-weighted and Fig 7b-Sagittal post contrast T1-weighted image showing pedunculated polypoidal enhancing lesion in the endocervical canal prolapsed from lower uterine segment endometrium. Fig 7c-Axial T2weighted image with FS and Fig 7d-Axial T1-weighted post-contrast image showing the same lesion with T2 hyper-intensity and post contrast enhancement. Fig 7e-Axial T2weighted and Fig 7f Axial T1-weighted post contrast images showing a small T2 intermediate signal intensity enhancing endometrial nodule representing a small polyp. Figure 8- Cervical cancer: Fig 8a-Axial T2-weighted and Fig 8b-Sagittal T2-weighted images showing a heterogeneous cervical mass hypointense on T2-weighted image and extending into the medial third of parametrium (arrows in Fig 8a) and upper third of vagina as seen in Fig 8b. Fig 8c-Sagittal ADC map and Fig 8d-Sagittal T1-weighted post-contrast images showing diffusion restriction and heterogeneous enhancement in the mass. Figure 9- Endometrial cancer: Fig 9a-Axial T2-weighted image and Fig 9b-ADC map showing endometrial mass with mild hyper-intensity on T2-weighted and diffusion restriction on the ADC map. Fig 9c-Sagittal Post-contrast T1-weighted and Fig 9d-Axial T1-weighted post-contrast images show irregular endometrial mass with heterogeneous enhancement that extends deep into the myometrium.

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Figure 10- Endometrial stromal sarcoma: Heterogeneous T2 hypo-intense enhancing endometrial mass lesion (arrows in Fig 10a and 10b) with fundal myometrial invasion and diffusion restriction (arrows in Fig 10c and 10d). Uterine Ewing’s sarcoma - A large uterine mass confined to the uterus showing heterogeneous T2 signal with multiple areas of T2 hyperintensity (arrows in Fig 10e) with heterogeneous enhancement (arrows in Fig 10f). Figure 11- Functional ovarian cyst: Fig 11a-Axial T2-weighted and Fig 11b-Axial post contrast T1-weighted fat saturated images showing unilocular cystic lesion (arrows) without enhancing nodules. Also sowing mild pelvic fluid (arrowheads) which is likely physiologic. Figure 12- Haemorrhagic cyst: Fig 12a-Axial T2-weighted and Fig 12b-Axial postcontrast T1-weighted images showing complex right ovarian lesion showing peripheral T2 hypointense (arrow in Fig 12a) non enhancing areas (arrow in Fig 12b) suggestive haemorrhagic products. Figure 13- Endometriosis: Fig 13a-Axial T1-weighted, Fig 13b-Axial T2-weighted and Fig 13c-Coronal T2-weighted images showing bilateral complex adnexal cysts with T1 hyperintensity (arrows in a) and variable T2 hypointensity, also called T2 shading (arrow in b), suggestive of multiple ovarian endometriomas with various stages of recurrent haemorrhage/proteinaceous contents. Fig 13d-Axial T1-weighted and Fig 13e-Axial T1weighted post-contrast subtraction images showing T1 hyperintense complex cystic lesions without enhancing nodules. Fig 13f-Pelvic USG of the same patient confirms the

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same with diffuse hyperechoic filling of one of the cystic locule suggestive of endometrioma. Figure 14- Serous cystadenoma ovary: Fig 14a-Axial T2-weighted and Fig 14b-Axial post contrast T1-weighted images showing bilocular cystic lesion (arrows) without enhancing nodules. Ovarian Dermoid: Fig 14c, d-Coronal T2-weighted images with and without fat supression showing a complex right ovarian mass with macroscopic fat showing signal loss on the fat saturated sequences (arrows). Figure 15- Malignant ovarian tumor: Fig 15a-Axial T2-weighted and Fig 15b-coronal T2-weighted images showing complex right pelvic mass with solid enhancing nodules (Fig 15c) and malignant ascites (Fig 15d). Figure 16- Krukenberg tumors-ovarian metastasis: Fig 16a-Axial T1-weighted and Fig 16b-axial T2-weighted images showing bilateral solid ovarian masses with heterogeneous enhancement (Fig 16c). The primary mass was located in the stomach and demonstrated irregular wall thickening involving fundus (Fig 16d). Figure 17- Rectal cancer: Fig 17a-Pictorial depiction of T staging of the tumor with relevant rectal anatomy. Fig 17b-Axial T2WI and Fig 17c-Axial T1-weighted postcontrast images showing a large high rectal mass extending anteriorly up to peritoneal reflection (Arrows in Fig 17b). Fig 17d and Fig 17e- Axial DWI images show restricted diffusion in the primary mass and multiple perirectal lymph nodes. Fig 17e-Axial T2weighted image showing a large rectal mass extending anteriorly to involve the urinary bladder (T4 disease), in another patient.

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Figure 18- Rectal GIST: Fig 18a-Axial T2-weighted and Fig 18b-Coronal T2-weighted images showing large exophytic low rectal mass with mild diffuse heterogeneous enhancement (Fig 18c and Fig 18d). Figure 19- Tailgut cyst: Fig 19a-Axial T2-weighted image and Fig 19b-Axial ADC map showing a minimally complex cystic lesion in pre-coccygeal region. Figure 20- Nerve sheath tumor: Fig 20a-Coronal T2-weighted, Fig 20b- Axial post contrast and Fig 20c -Sagittal post contrast images showing a large presacral mass with predominant T2 hyperintensity with heterogeneous enhancement and foci of nonenhancement suggestive of cystic/necrotic areas.

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